Structural Steel For Through-Surface Hardening

Abstract

The invention refers to development of chemical composition of perlite-class structural steels hardened by thermal treatment—through-surface hardening (TSH). The technical result is to obtain low and specified hardenability 3rd generation LH (SH) steels with a finer austenite grain ##11-13 GOST5639 (ASTM), even more stable preset hardenability (DI) with a substantially smaller To obtain a finer austenite grain and more stable hardenability—DI, with a substantially smaller deviation range and hardened layer depth directly obtained on parts subjected to TSH, as well as the possibility of machining thinner, smaller and other parts with the through-surface and through-thickness hardening. To achieve the technical result, structural steel was proposed for through-surface hardening with the following components ratio, weight %: carbon—0.15-1.2; manganese—not more than 1.8; silicon—not more than 1.8; chrome—not more than 1.8; nickel—not more than 1.8; molybdenum—not more than 0.5; tungsten—not more than 1.5; boron—not more than 0.007; copper—not more than 0.3; aluminum—0.03-0.1; nitrogen—not more than 0.1; titanium—not more than 0.4; vanadium,—not more than 0.4; zirconium—not more than 0.4; niobium—not more than 0.1; tantalum—not more than 0.1; calcium—not more than 0.03; sulphur—not more than 0.035; phosphorus—not more than 0.035; iron and unavoidable admixtures—rem., with ideal diameter determined by the following mathematical formula: Dkp.=K·√C·(1+4.1·Mn)·(1+0.65·Si)·(1+2.33·Cr)·(1+0.52·Ni)·(1+0.27·Cu)··(1+3.14·Mo)·(1+1.05·W)·[1+1.5(0.9−C)]·(1−0.45C′)·(1−0.3Ti)·(1−0.35V)·(1−0.25Al), Where: Dcr is the ideal diameter, mm, K is the coefficient whose value depends on the actual austenite grain size according to the ASTM, GOST5639; C, Mn, Si, Cr, Ni, Cu, Mo, W are components, weight %, contained in the austenite solid solution at the final heating temperature preceding hardening cooling, [1+1.5(0.9−C)] is the multiplier taken into account only if boron is present in steel in the amount of 0.002-0.007 weight %; C′, Ti, V, Al are components, weight %, not contained in the austenite solid solution, but present in the form of structurally-free secondary carbonitride phases at the final heating temperature preceding hardening cooling, C′ is carbon in the excessive cementite of hypereutectoid steel.

1 . Structural steel for through-surface hardening containing carbon, manganese, silicon, chrome, nickel, copper, aluminum , titanium, vanadium, niobium, tantalum, calcium, sulphur, phosphorus, iron and unavoidable admixtures, with a distinction that it additionally contains molybdenum, tungsten, boron, nitrogen and zirconium with the following component ratio, weight %: 
       
         
           
                 
                 
                 
               
                     
                     
                 
                     
                   Carbon 
                   .15-1.2 
                 
                     
                   Manganese 
                   not more than 1.8 
                 
                     
                   Silicon 
                   not more than 1.8 
                 
                     
                   Chrome 
                   not more than 1.8 
                 
                     
                   Nickel 
                   not more than 1.8 
                 
                     
                   Molybdenum 
                   not more than .5 
                 
                     
                   Tungsten 
                   not more than 1.5 
                 
                     
                   Boron 
                   .not more than .007 
                 
                     
                   Copper 
                   not more than .3 
                 
                     
                   Aluminum 
                   .03-.1 
                 
                     
                   Nitrogen 
                   not more than .1 
                 
                     
                   Titanium 
                   not more than .4 
                 
                     
                   Vanadium 
                   not more than .4 
                 
                     
                   Zirconium 
                   not more than .4 
                 
                     
                   Niobium 
                   not more than .1 
                 
                     
                   Tantalum 
                   not more than .1 
                 
                     
                   Calcium 
                   not more than .03 
                 
                     
                   Sulphur 
                   not more than .035 
                 
                     
                   Phosphorus 
                   not more than .035 
                 
                     
                     
                 
             
                
               
               
                
                
                
                
                
                
                
                
                
                
                
                
                
                
                
                
                
                
                
                
               
            
           
         
       
       Iron and unavoidable admixtures—remaining. 
     
     
         2 . Steel as per Item  1 , with a distinction that its ideal hardening diameter (DI) is determined by the mathematical expression:
   Dkp.=K·√C·(1+4.1·Mn)·(1+0.65·Si)·(1+2.33·Cr)·(1+0.52·Ni)·(1+0.27·Cu)·(1+3.14·Mo)·(1+1.05·W)·[1+1.5(0.9−C)]·(1−0.45C′)·(1−0.3Ti)·(1−0.35V)·(1−0.25Al),
   
       where
 Dcr is the ideal diameter, mm, 
 K is the coefficient that depends on the grain sizes #8-13 of the real austenite according to the ASTM scale, GOST5639, and is, correspondingly, equal to: 5.4 for #13 grain, 5.8 for #12, 6.25 for #11, 6.75 for #10, 7.3 for #9, 7.9 for #8, 8.5 for #7. 9.2 for #6; 
 C, Mn, Si, Cr, Ni, Cu, Mo, W are the components, weight %, contained in the austenite solid solution at the final heating temperature preceding hardening cooling; 
 [1+1.5(0.9−C)] is the multiplier taken into account only if boron is present in steel in the amount of 0.002-0.007 weight %; 
 C′, Ti, V, Al are components, weight %, not contained in the austenite solid solution, but present in the form of structurally-free secondary carbonitride phases at the final heating temperature preceding hardening cooling, in which case C′ is the weight % carbon in the excessive hypereutectoid steel cementite 
 
     
     
         3 . Steel as per Item  1 , with a distinction that its ideal diameter by the specified chemical composition, with the same grain size, has the following values:
 for 6-15 mm DI—with the deviation of not greater than 2 mm;   for 16-50 mm DI—with the deviation of not greater than 5 mm;   for 51-100 mm DI—with the deviation of not greater than 10 mm;   for over 100 mm DI—with the deviation of not greater than 50 mm.   
     
     
         4 . Steel as per Item  1 , with a distinction that in order to prevent hot-brittleness the combined content of manganese, titanium and zirconium is more than six times the maximum sulphur content.