Method for modifying and thereby improving the corrosion resistance and hardness of workpieces of ferritic steel
First Claim
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1. A method for modifying and thereby improving the corrosion resistance and hardness of workpieces of ferritic steel, comprising the steps of:
- forming a workpiece core from a ferritic chrome steel having a chrome percentage by weight of at least 13%;
providing said workpiece core with an outer layer of nickel, said outer layer having a thickness of at least 5 μ
m; and
diffusion annealing said workpiece under an oxygen-free environment a at at least 850°
C. so as to form an intermediate austenitic chrome-nickel alloyed layer between said chrome steel core and said outer layer of nickel which provides said workpiece with a desired corrosion resistance while said chrome steel core is changed from ferritic chrome steel to martensitic chrome steel which provides said workpiece with a desired degree of hardness.
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Abstract
The invention relates to a method for making workpieces of ferritic steel, such as drilling screws wherein the workpiece is made of a transformable chrome steel having a chrome percentage of at least 13%, whereupon a workpiece receives a coating from nickel or a nickel or cobald alloy having a thickness of at least 5 μm, and subsequently the workpiece is heat treated under oxygen free environment at at least 850° C. so as to obtain a desired hardness and corrosion resistance.
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Citations
19 Claims
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1. A method for modifying and thereby improving the corrosion resistance and hardness of workpieces of ferritic steel, comprising the steps of:
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forming a workpiece core from a ferritic chrome steel having a chrome percentage by weight of at least 13%; providing said workpiece core with an outer layer of nickel, said outer layer having a thickness of at least 5 μ
m; anddiffusion annealing said workpiece under an oxygen-free environment a at at least 850°
C. so as to form an intermediate austenitic chrome-nickel alloyed layer between said chrome steel core and said outer layer of nickel which provides said workpiece with a desired corrosion resistance while said chrome steel core is changed from ferritic chrome steel to martensitic chrome steel which provides said workpiece with a desired degree of hardness. - View Dependent Claims (3, 4, 5, 6, 7)
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2. A method for modifying and thereby improving the corrosion resistance and hardness of workpieces of ferritic steel, comprising the steps of:
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forming a workpiece core from a ferritic steel containing a percentage of nickel or molybdenum; providing said workpiece core with an outer layer of chrome having a thickness of at least 5 μ
m; anddiffusion annealing said workpiece under an oxygen-free environment at at least 850°
C. so as to form an intermediate austenitic nickel-chrome or molybdenum-chrome alloyed layer between said nickel or molybdenum steel core and said outer layer of chrome which provides said workpiece with a desired degree of corrosion resistance while said nickel or molybdenum steel core is changed from ferritic nickel or molybdenum steel to martensitic nickel or molybdenum steel which provides said workpiece with a desired degree of hardness.
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8. A method for modifying and thereby improving the corrosion resistance and hardness of workpieces of ferritic steel, comprising the steps of:
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forming a workpiece core from a ferritic chrome steel having a chrome percentage by weight of at least 13%; providing said workpiece core with an outer layer of a nickel alloy having a thickness of at least 5 μ
m; anddiffusion annealing said workpiece under an oxygen-free environment at at least 850°
C. so as to form an intermediate austenitic chrome-nickel alloyed layer between said chrome steel core and said outer layer of said nickel alloy which provides said workpiece with a desired corrosion resistance while said chrome steel core is changed from ferritic chrome steel to martensitic chrome steel which provides said workpiece with a desired degree of hardness. - View Dependent Claims (9, 10, 11, 12, 13)
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14. A method for modifying and thereby improving the corrosion resistance and hardness of workpieces of ferritic steel, comprising the steps of:
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forming a workpiece core from a ferritic chrome steel having a chrome percentage by weight of at least 13%; providing said workpiece core with an outer layer of a cobalt alloy having a thickness of at least 5 μ
m; anddiffusion annealing said workpiece under an oxygen-free environment at at least 850°
C. so as to form an intermediate austenitic chrome-cobalt alloyed layer between said chrome steel core and said outer layer of said cobalt alloy which provides said workpiece with a desired corrosion resistance while said chrome steel core is changed from ferritic chrome steel to martensitic chrome steel which provides said workpiece with a desired degree of hardness. - View Dependent Claims (15, 16, 17, 18, 19)
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Specification