Case-hardened stainless steel foundry alloy and methods of making the same

Abstract

A case-hardened stainless steel part and method of making the same are disclosed. The part comprises a case defining a first layer proximate the outer surface of the part and a core defining a second layer adjacent the case and distal from the outer surface. The core has a hardness of from about 80 on the Rockwell Hardness B Scale to about 50 on the Rockwell Hardness C Scale. The case has a hardness of not less than about 30 equivalence on the Rockwell Hardness C Scale.

1 . A case-hardened, cast part formed from a stainless steel alloy, the alloy comprising: 
 chromium in an amount of from about 15.5 to about 18.5 percent by weight of the alloy;    carbon in an amount of from about 0.13 to about 0.29 percent by weight of the alloy;    manganese in an amount up to about 1.5 percent by weight of the alloy;    silicon in an amount of from about 0.25 to about 1.5 percent by weight of the alloy;    molybdenum in an amount up to about 1.0 percent by weight of the alloy; and    iron present in a remaining amount of the alloy;    wherein said cast part has an outer surface and a case, said case defining a first layer of said part proximate said surface, said cast part further comprising a core, said core defining a second layer of said cast part adjacent to said case and distal from said surface, wherein said core has a hardness of from about HRB 80 to HRC 50 and said case has a hardness of not less than about HRC 30 equivalence.    
     
     
         2 . The cast part of  claim 1 , wherein said case further has a thickness of from about 0.002 inches to about 0.035 inches.  
     
     
         3 . The cast part of  claim 1 , wherein said part has a yield strength of not more than about 125,000 psi.  
     
     
         4 . The cast part of  claim 1 , wherein said amount of chromium is from about 15.5 to about 18.0 percent by weight of the alloy.  
     
     
         5 . The cast part of  claim 1 , wherein said amount of chromium is from about 16.5 to about 18.0 percent by weight of the alloy.  
     
     
         6 . The cast part of  claim 1 , wherein said amount of carbon is from about 0.13 to about 0.24 percent by weight of the alloy.  
     
     
         7 . The cast part of  claim 1 , wherein said amount of carbon is from about 0.13 to about 0.21 percent by weight of the alloy.  
     
     
         8 . The cast part of  claim 1 , wherein said amount of manganese is from about 0.3 to about 1.0 percent by weight of the alloy.  
     
     
         9 . The cast part of  claim 1 , wherein said amount of manganese is from about 0.3 to about 0.6 percent by weight of the alloy.  
     
     
         10 . The cast part of  claim 1 , wherein said amount of molybdenum is from about 0.25 to about 0.5 percent by weight of the alloy.  
     
     
         11 . The cast part of  claim 1 , wherein said amount of silicon is from about 0.3 to about 1.0 percent by weight of the alloy.  
     
     
         12 . The cast part of  claim 1 , wherein said amount of silicon is from about 0.3 to about 0.8 percent by weight of the alloy.  
     
     
         13 . A golf club head formed from the cast part of  claim 1 .  
     
     
         14 . The golf club head of  claim 13 , comprising a wedge-shaped striking surface.  
     
     
         15 . The cast part of  claim 1 , wherein the case has a carbon concentration and the core has a carbon concentration, said case carbon concentration being higher than said core carbon concentration.  
     
     
         16 . A case-hardened, cast part formed from a stainless steel alloy, the alloy comprising: 
 chromium in an amount of from about 15.5 to about 18.5 percent by weight of the alloy;    wherein said cast part has an outer surface and a case defining a first layer proximate said outer surface, said part further comprising a core defining a second layer of said part adjacent said case and distal from said surface, wherein said core has a hardness of from about HRB 80 to about HRC 50 and said case has a hardness of not less than about HRC 30 equivalence.    
     
     
         17 . The cast part of  claim 16 , wherein the alloy further comprises carbon in an amount of from about 0.13 to about 0.29 percent by weight of the alloy.  
     
     
         18 . The cast part of  claim 17 , wherein said amount of carbon is from about 0.13 to about 0.21 percent by weight of the alloy.  
     
     
         19 . The cast part of  claim 16 , wherein the alloy further comprises manganese in an amount up to about 1.5 percent of the alloy.  
     
     
         20 . The cast part of  claim 19 , wherein said amount of manganese is from about 0.3 to about 0.6 percent by weight of the alloy.  
     
     
         21 . The cast part of  claim 16 , wherein the alloy further comprises silicon in an amount of from about 0.25 to about 1.5 percent by weight of the alloy.  
     
     
         22 . The cast part of  claim 21 , wherein said amount of silicon is from about 0.3 to about 0.8 percent by weight of the alloy.  
     
     
         23 . The cast part of  claim 16 , wherein the alloy further comprises molybdenum in an amount up to about 1.0 percent by weight of the alloy.  
     
     
         24 . The cast part of  claim 23 , wherein said amount of molybdenum is from about 0.25 to about 0.5 percent by weight of the alloy.  
     
     
         25 . The cast part of  claim 16 , wherein said amount of chromium is from about 16.5 to 18 percent by weight of the alloy.  
     
     
         26 . A golf club head formed from the stainless steel cast part of  claim 16 .  
     
     
         27 . The golf club head of  claim 26 , wherein said golf club head comprises a wedge-shaped striking surface.  
     
     
         28 . The cast part of  claim 16 , wherein said case has a thickness of from about 0.002 inches to about 0.035 inches.  
     
     
         29 . The cast part of  claim 16 , wherein the case has a carbon concentration and the core has a carbon concentration, said case carbon concentration being higher than said core carbon concentration.  
     
     
         30 . A method of forming a case-hardened, stainless steel cast part, comprising the steps of: 
 providing a cast part formed from an alloy comprising chromium in an amount of from about 15.5 to about 18.5 percent by weight of the alloy; and    carburizing said cast part at a temperature of from about 1600° F. to about 1900° F. for a period of from about 1 hour to less than about 2 hours.    
     
     
         31 . The method of  claim 30 , further comprising homogenizing said cast part at a temperature of from about 1900° F. to about 2100° F. for a period of about 1 to about 4 hours.  
     
     
         32 . The method of  claim 31  wherein said homogenizing temperature is about 2100° F.  
     
     
         33 . The method of  claim 31 , wherein said period of homogenizing is about 1.5 hours.  
     
     
         34 . The method of  claim 30 , further comprising preheating said cast part at a temperature of from about 1100° F. to about 1400° F. for a period of about 30 minutes to 1 hour before said carburizing step.  
     
     
         35 . The method of  claim 34 , wherein said preheating temperature is about 1200° F.  
     
     
         36 . The method of  claim 34 , wherein said period of preheating is about 30 minutes.  
     
     
         37 . The method of  claim 30 , further comprising quenching said cast part with a fluid having a temperature of from about 100° F. to about 200° F. for a period of about 5 to about 15 minutes.  
     
     
         38 . The method of  claim 37 , wherein said fluid is oil.  
     
     
         39 . The method of  claim 30 , further comprising cooling said cast part at a temperature of not more than about −100° F. for a period of about 1 to about 3 hours.  
     
     
         40 . The method of  claim 39 , wherein said cooling temperature is about −100° F.  
     
     
         41 . The method of  claim 39 , wherein said cooling period is about 2 hours.  
     
     
         42 . The method of  claim 30 , further comprising tempering said cast part at a temperature of from about 200 to about 600° F. for a period of about 1 to about 3 hours.  
     
     
         43 . The method of  claim 42 , wherein said tempering temperature is about 300° F.  
     
     
         44 . The method of  claim 30 , wherein the alloy further comprises carbon in an amount of from about 0.13 to about 0.29 percent by weight of the alloy.  
     
     
         45 . The method of  claim 44 , wherein said amount of carbon is from about 0.13 to about 0.24 percent by weight of the alloy.  
     
     
         46 . The method of  claim 44 , wherein said amount of carbon is from about 0.13 to about 0.21 percent by weight of the alloy.  
     
     
         47 . The method of  claim 30 , wherein the alloy further comprises manganese in an amount up to about 1.5 percent by weight of the alloy.  
     
     
         48 . The method of  claim 47 , wherein said amount of manganese is from about 0.3 to about 1.0 percent by weight of the alloy.  
     
     
         49 . The method of  claim 47 , wherein said amount of manganese is from about 0.3 to about 0.6 percent by weight of the alloy.  
     
     
         50 . The method of  claim 30 , wherein the alloy further comprises silicon in an amount of from about 0.25 to about 1.5 percent by weight of the alloy.  
     
     
         51 . The method of  claim 50 , wherein said amount of silicon is from about 0.3 to about 1.0 percent by weight of the alloy.  
     
     
         52 . The method of  claim 50 , wherein said amount of silicon is from about 0.3 to about 0.8 percent by weight of the alloy.  
     
     
         53 . The method of  claim 30 , wherein the alloy further comprises molybdenum in an amount up to about 1.0 percent of the alloy.  
     
     
         54 . The method of  claim 53 , wherein the amount of molybdenum is from about 0.25 to about 0.5 percent by weight of the alloy.  
     
     
         55 . The method of  claim 30 , wherein said amount of chromium is from about 15.5 to about 18.0 percent by weight of the alloy.  
     
     
         56 . The method of  claim 30 , wherein said amount of chromium is from about 16.5 to about 18.0 percent by weight of the alloy.  
     
     
         57 . The method of  claim 30 , wherein said period of carburizing is about 1 hour.  
     
     
         58 . The method of  claim 30 , wherein said carburizing temperature is about 1800° F.  
     
     
         59 . A method of forming a golf club head according to the method of  claim 30 , wherein said cast part is prepared by forming the alloy into the shape of a golf club head.  
     
     
         60 . A golf club head prepared by the method of  claim 59 .  
     
     
         61 . The method of  claim 30 , wherein said carburizing step forms a case in the cast part defining a first layer and a core in the cast part defining a second layer, wherein said core has a hardness of from about HRB 80 to about HRC 50 and said case has a hardness of not less than about HRC 30 equivalence.  
     
     
         62 . A method of making a golf club head, comprising: 
 a. providing a steel alloy comprising chromium in an amount of from about 15.5 to about 18.5 percent by weight of the alloy;    b. forming said alloy into a part having the shape of a golf club head;    c. preheating said part;    d. carburizing said part;    e. quenching said part with a fluid;    f. cooling said part; and    g. tempering said part.    
     
     
         63 . The method of  claim 62 , wherein said forming step is performed by investment casting.  
     
     
         64 . The method of  claim 62 , wherein said carburizing step is conducted at a temperature of from about 1600° F. to 1900° F. for a period of about 1 to 3 hours.  
     
     
         65 . The method of  claim 64 , wherein said carburizing temperature is about 1800° F. and said period of carburizing is about 1 hour.  
     
     
         66 . The method of  claim 62 , wherein said amount of chromium is from about 16.5 to about 18 percent of the alloy.  
     
     
         67 . The method of  claim 62 , further comprising homogenizing said part.  
     
     
         68 . The method of  claim 62 , wherein said preheating step is conducted at a temperature of from about 1100° F. to about 1400° F. for a period of about 30 minutes to about 1 hour.  
     
     
         69 . The method of  claim 68 , wherein said preheating temperature is about 1200° F.  
     
     
         70 . The method of  claim 62 , wherein said fluid has a temperature of from about 100° F. to about 200° F. during said quenching step.  
     
     
         71 . The method of  claim 62 , wherein said cooling step is conducted at a temperature of not more than about −100° F. for a period of about 1 to about 3 hours.  
     
     
         72 . The method of  claim 71 , wherein said cooling temperature is about −100° F. and said period of cooling is about 2 hours.  
     
     
         73 . The method of  claim 62 , wherein said tempering step is conducted at a temperature of from about 200° F. to about 600° F. for a period of about 1 to about 3 hours.  
     
     
         74 . The method of  claim 62 , wherein said tempering temperature is about 300° F.  
     
     
         75 . The method of  claim 62 , wherein said alloy further comprises carbon in an amount of from about 0.13 to about 0.29 percent by weight of the alloy.  
     
     
         76 . The method of  claim 75 , wherein said amount of carbon is from about 0.13 to about 0.21 percent by weight of the alloy.  
     
     
         77 . The method of  claim 62 , wherein said alloy further comprises manganese in an amount up to about 1.5 percent by weight of the alloy.  
     
     
         78 . The method of  claim 62 , wherein said amount of manganese is from about 0.3 to about 0.6 percent by weight of the alloy.  
     
     
         79 . The method of  claim 62 , wherein said alloy further comprises silicon in an amount of from about 0.25 to about 1.5 percent by weight of the alloy.  
     
     
         80 . The method of  claim 79 , wherein said amount of silicon is from about 0.3 to about 0.8 percent by weight of the alloy.  
     
     
         81 . The method of  claim 62 , wherein said alloy further comprises molybdenum in an amount up to about 1.0 percent by weight of the alloy.  
     
     
         82 . The method of  claim 81 , wherein said amount of molybdenum is from about 0.3 to about 0.8 percent by weight of the alloy.  
     
     
         83 . The method of  claim 62 , wherein said amount of chromium is from about 16.5 to about 18 percent by weight of the alloy.  
     
     
         84 . The method of  claim 62 , wherein said part includes an outer surface, and wherein said carburizing step forms a case defining a first layer of said part proximate said outer surface and a core defining a second layer of said part adjacent to said case and distal from said surface, and wherein said core has a hardness of from about HRB 80 to about HRC 50 and said case has a hardness of not less than about HRC 30 equivalence.  
     
     
         85 . The method of  claim 62 , further comprising polishing said part.  
     
     
         86 . The method of  claim 62 , wherein said step of forming said alloy into a part having the shape of a golf club head includes forming said alloy into a part having a wedge-shaped striking surface.  
     
     
         87 . The method of  claim 62 , wherein said fluid is oil.  
     
     
         88 . The method of  claim 63 , wherein said investment casting comprises preparing a casting mold by (i) providing a temporary preform shaped in the form of a golf club head; (ii) surrounding said preform with a refractory slurry; (iii) hardening said refractory slurry; (iv) melting said preform; (v) and removing said melted preform from said hardened refractory slurry, wherein the hardened refractory slurry is the casting mold.  
     
     
         89 . The method of  claim 88 , wherein said forming step further comprises heating said alloy and pouring it into said casting mold.  
     
     
         90 . The method of  claim 67 , wherein said homogenizing step is conducted at a temperature of from about 1900° F. to about 2100° F. for a period of from about 1 to 4 hours.  
     
     
         91 . The method of  claim 67 , wherein said homogenizing step is conducted at a temperature of about 2100° F. for a period of about 1.5 hours.  
     
     
         92 . A method of making a golf club head, comprising: 
 a. preparing a casting mold by (i) providing a temporary preform shaped in the form of a golf club head, (ii) surrounding said preform with a refractory slurry, (iii) hardening said refractory slurry, (iv) melting said preform, and (iv) removing said melted preform from said hardened refractory slurry, wherein the hardened refractory slurry is the casting mold;    b. combining chromium in an amount of from about 16.5 to about 18.0 percent by weight, carbon in an amount of from about 0.13 to about 0.21 percent by weight, manganese in an amount of from about 0.3 to about 0.6 percent by weight, silicon in an amount of from about 0.3 to about 0.8 percent by weight and molybdenum in an amount of from about 0.25 to about 0.5 percent by weight, with iron present in a remaining amount;    c. melting the combined ingredients to form a mixture;    d. pouring the mixture into said casting mold to form a cast part;    e. removing said cast part from said casting mold, said cast part having an outer surface;    f. homogenizing the cast part at a temperature of about 2100° F. for about 1.5 hours;    g. preheating the cast part at a temperature of about 1200° F. for a period of about 30 minutes to about 1 hour;    h. carburizing said cast part at a temperature of about 1800° F. for about 1 hour, thereby forming a case having a carbon concentration, said case defining a first layer of said cast part proximate said outer surface, and a core having a carbon concentration, said core defining a second layer of said cast part adjacent to said case and distal from said surface, said case carbon concentration being higher than said core carbon concentration;    i. quenching said cast part with a fluid having a temperature of from about 100° F. to about 200° F. for a period of about 5 to about 15 minutes;    j. cooling said cast part at a temperature of about −100° F. for about 2 hours;    k. tempering said cast part at a temperature of about 300° F. for about 1 to about 3 hours; and    l. polishing said part;    wherein said core has a hardness of from about HRB 80 to about HRC 50, said case has a hardness of not less than about HRC 30 equivalence and said part has a yield strength of not more than about 125,000 psi.    
     
     
         93 . A golf club head prepared by: 
 a. preparing a casting mold by (i) providing a temporary preform shaped in the form of a golf club head, (ii) surrounding said preform with a refractory slurry, (iii) hardening said refractory slurry, (iv) melting said preform, and (iv) removing said melted wax mold from said hardened refractory slurry, wherein the hardness refractory slurry is the casting mold;    b. combining chromium in an amount of from about 16.5 to about 18.0 percent by weight, carbon in an amount of from about 0.13 to about 0.21 percent by weight, manganese in an amount of from about 0.3 to about 0.6 percent by weight, silicon in an amount of from about 0.3 to about 0.8 percent by weight and molybdenum in an amount of from about 0.25 to about 0.5 percent by weight, with iron present in a remaining amount;    c. melting the combined ingredients to form a mixture;    d. pouring the mixture into said casting mold to form a cast part;    e. removing said cast part from said casting mold, said cast part having an outer surface;    f. homogenizing the cast part at a temperature of about 2100° F. for about 1.5 hours;    g. preheating the cast part at a temperature of about 1200° F. for a period of about 30 minutes to about 1 hour;    h. carburizing the cast part at a temperature of about 1800° F. for about 1 hour, thereby forming a case having a carbon concentration, said case defining a first layer of said cast part proximate said outer surface, and a core having a carbon concentration, said core defining a second layer of said cast part adjacent to said case and distal from said surface, said case carbon concentration being higher than said core carbon concentration;    i. quenching said cast part with a fluid having a temperature of from about 100° F. to 200° F. for a period of about 5 to 15 minutes;    j. cooling said cast part at a temperature of about −100° F. for about 2 hours;    k. tempering said cast part at a temperature of about 300° F. for about 1 to about 3 hours; and    l. polishing said part;    wherein said core has a hardness of from about HRB 80 to about HRC 50, said case has a hardness of not less than about HRC 30 equivalence, and said part has a yield strength of not more than about 125,000 psi.    
     
     
         94 . A case-hardened, stainless steel cast part prepared by: 
 a. providing a casting mold;    b. combining chromium in an amount of from about 16.5 to about 18.0 percent by weight, carbon in an amount of from about 0.13 to about 0.21 percent by weight, manganese in an amount of from about 0.3 to about 0.6 percent by weight, silicon in an amount of from about 0.3 to about 0.8 percent by weight and molybdenum in an amount of from about 0.25 to about 0.5 percent by weight, with iron present in a remaining amount;    c. melting the combined ingredients to form a stainless steel mixture;    d. pouring the stainless steel mixture into said casting mold to form a cast part;    e. removing said cast part from said casting mold, said cast part having a surface;    f. homogenizing the cast part at a temperature of about 2100° F. for about 1.5 hours;    g. preheating the cast part at a temperature of about 1200° F. for a period of about 30 minutes to about 1 hour;    h. carburizing the cast part at a temperature of about 1800° F. for about 1 hour thereby forming a case having a carbon concentration, said case defining a first layer of said cast part proximate said surface, and a core having a carbon concentration, said core defining a second layer of said cast part adjacent to said case and distal from said surface, said case carbon concentration being higher than said core carbon concentration;    i. quenching said cast part with oil having a temperature of from about 100° F. to about 200° F. for a period of about 5 to about 15 minutes;    j. cooling said cast part at a temperature of about −100° F. for about 2 hours;    k. tempering said cast part at a temperature of about 300° F. for about 1 to about 3 hours; and    l. polishing said cast part;    wherein said core has a hardness of from about HRB 80 to about HRC 50, said case has a hardness of not less than about HRC 30 equivalence, and said part has a yield strength of not more than about 125,000 psi.    
     
     
         95 . A method of case hardening a steel cast part, comprising: 
 a. providing a cast steel part having an outer surface;    b. homogenizing said part at a temperature of about 2100° F. for about 1.5 hours;    c. preheating said part at a temperature of about 1200° F. for a period of about 30 minutes to about 1 hour;    d. carburizing said part at a temperature of about 1800° F. for about 1 hour, thereby forming a case defining a first layer and a core defining a second layer;    e. quenching said part with oil having a temperature of from about 100° F. to about 200° F. for a period of about 5 to about 15 minutes;    f. refrigerating said part at a temperature of about −100° F. for about 2 hours;    g. tempering said part at a temperature of about 300° F. for about 1 to about 3 hours; and    h. polishing said cast steel part;    wherein said core has a hardness of from about HRB 80 to about HRC 50 and said case has a hardness of not less than about HRC 30 equivalence.    
     
     
         96 . The cast part of  claim 1 , wherein said core has a hardness of from about HRC 20 to about HRC  34 .  
     
     
         97 . The cast part of  claim 1 , wherein said case has a hardness of not less than about HRC 50 equivalence.  
     
     
         98 . The cast part of  claim 16 , wherein said core has a hardness of from about HRC  20  to about HRC  34 .  
     
     
         99 . The cast part of  claim 16 , wherein said case has a hardness of not less than about HRC  50  equivalence.