A hydrogen embrittlement resistance coated steel

Abstract

A method of production of a coated steel substrate including of the steps to have a steel substrate; performing electroplating of the steel substrate with an electroplating solution having a pH of from 2 to 6 and containing 100 g/l to 500 g/l of NiSO4 and 1 g/l to 15 g/l of MoS2, by applying a current density from 15 A/dm 2 to 45 A/dm 2 during 30 seconds to 300 seconds to generate a layer of Ni—MoS2 coating; thereafter, rinsing the steel substrate and drying it to obtain a coated steel substrate.

What is claimed is: 
     
         1 - 12 . (canceled) 
     
     
         13 . A method of production of a coated steel substrate comprising the following steps:
 providing a steel substrate;   electroplating the steel substrate with an electroplating solution having a pH of from 2 to 6 and containing 100 g/l to 500 g/l of NiSO4 and 1 g/l to 15 g/l of MoS2, by applying a current density from 15 A/dm 2  to 45 A/dm 2  during 30 seconds to 300 seconds to generate a layer of Ni—MoS2 coating;   rinsing the electroplated steel substrate; and   drying the electroplated steel substrate to obtain a coated steel substrate.   
     
     
         14 . The method as recited in  claim 13  wherein the pH of the electroplating solution is from 2 to 5. 
     
     
         15 . The method as recited in  claim 13  wherein a concentration of NiSO4 in the electroplating solution is from 100 g/l to 400 g/l. 
     
     
         16 . The method as recited in  claim 13  wherein a concentration of MoS2 in the electroplating solution is from 2 g/l to 14 g/l. 
     
     
         17 . The method as recited in  claim 13  wherein the steel substrate submitted to the electroplating step is a cold rolled steel sheet obtained though the following steps:
 providing a semi-finished product of steel; 
 reheating the semi-finished product to a temperature from 1000° C. to 1280° C.; 
 rolling the semi-finished product in the austenitic range with a hot rolling finishing temperature above 850° C. to obtain a hot rolled steel sheet; 
 cooling the sheet at an average cooling rate above 30° C./s to a coiling temperature below 650° C. and coiling the hot rolled steel sheet; 
 cooling the hot rolled steel sheet to room temperature; 
 optionally performing a scale removal step on the hot rolled steel sheet; 
 optionally annealing the a hot rolled steel sheet at a temperature from 400° C. to 750° C.; 
 optionally performing a further scale removal step on the hot rolled steel sheet; 
 cold rolling the hot rolled steel sheet with a reduction rate from 35 to 90% to obtain a cold rolled steel sheet; 
 then performing annealing by heating the cold rolled steel sheet at a rate heating rate greater than 2° C./s to a soaking temperature which is from Ac1 to Ac3+100° C. where the cold rolled steel sheet is held for 10 seconds to 500 seconds; 
 then cooling the sheet at a rate greater than 5° C./s to a temperature below 550° C., wherein during the cooling the cold rolled steel sheet can optionally be held a temperature ranges from 150° C. to 500° C. for a time from 10 to 1000 seconds, to obtain a cold-rolled steel substrate; and 
 then acid pickling the cold rolled steel substrate is acid for 5 seconds to 100 seconds at a temperature range from 30° C. to 100° 
 
     
     
         18 . A coated steel substrate manufactured according to the method as recited in  claim 13 , wherein the Ni—MoS2 layer has a thickness of at least 0.1 micron and contains at least 0.3% by weight percentage of MoS2 particles. 
     
     
         19 . The coated steel substrate as recited in  claim 18  wherein the Ni—MoS2 layer has a thickness of at least 0.2 micron. 
     
     
         20 . The coated steel substrate as recited in  claim 18  wherein the Ni—MoS2 layer contains at least 0.4% by weight percentage of MoS2 particles. 
     
     
         21 . The coated steel substrate as recited in  claim 18  wherein a hydrogen embrittlement ratio of the coated steel substrate is less than 30%. 
     
     
         22 . The coated steel substrate as recited in  claim 18  wherein the coated steel substrate is a cold rolled steel sheet with a composition comprising the following elements, expressed in percentage by weight:
 0.05%≤C≤0.5%; 
 0.2%≤Mn≤5%; 
 0.1%≤Si≤2.5%; 
 0.01%≤Al≤2%; 
 0%≤S≤0.09%; 
 0.002%≤P≤0.09%; 
 0%≤N≤0.09%; 
 and optionally one or more of the following elements: 
 0%≤Cr≤1%; 
 0%≤Ni≤1%; 
 0%≤Cu≤1%; 
 0%≤Mo≤0.5%; 
 0%≤Nb≤0.1%; 
 0%≤Ti≤0.1%; 
 0%≤V≤0.1%; 
 0%≤B≤0.003%; 
 0%≤Mg≤0.010%; 
 0%≤Zr≤0.010%; 
 0.001%≤Ca≤0.005%; 
 a remainder of the composition being composed of iron and unavoidable impurities caused by processing. 
 
     
     
         23 . The coated steel substrate as recited in  claim 18  wherein the steel substrate has an ultimate tensile strength of 900 MPa or more, and a yield strength of 700 MPa or more. 
     
     
         24 . A method for manufacturing a structural part of a vehicle comprising the method as recited in  claim 13 .