Surface modified steel member with anti-corrosion properties and method for modifying surface of steel material

Abstract

A steel member with surface modified during manufacture has good anti-corrosion properties. The steel member includes a steel substrate, a metallic diffusion layer formed on the steel substrate, and an alloy deposition layer formed on the metallic diffusion layer. The steel substrate is made of low-carbon steel or low-carbon alloy steel. After cleaning and heating processes are applied, the metallic diffusion layer includes pearlite and ferrite crystals and hardness of the surface is also enhanced. The alloy deposition layer includes zinc ferrum alloy.

What is claimed is: 
     
         1 . A surface modified steel member with anti-corrosion properties, comprising:
 a steel substrate made of low-carbon steel or low-carbon alloy steel;   a metallic diffusion layer formed on the steel substrate, the metallic diffusion layer comprising pearlite crystals and ferrite crystals; and   an alloy deposition layer formed on the metallic diffusion layer opposite to the steel substrate, the alloy deposition layer comprising zinc ferrum alloys.   
     
     
         2 . The surface modified steel member of  claim 1 , wherein the steel substrate is not quenched and tempered, the metallic diffusion layer has a Micro Vickers Hardness greater than a Micro Vickers Hardness of the steel substrate, and the Micro Vickers Hardness of the steel substrate is in a range from 150 to 260, and the Micro Vickers Hardness of the metallic diffusion layer is in a range from 200 to 400. 
     
     
         3 . The surface modified steel member of  claim 1 , wherein the steel substrate is quenched and tempered, the metallic diffusion layer has a Micro Vickers Hardness not greater than a Micro Vickers Hardness of the steel substrate, the Micro Vickers Hardness of each of the steel substrate and the metallic diffusion layer is in a range from 240 to 450. 
     
     
         4 . The surface modified steel member of  claim 3 , wherein the metallic diffusion layer further comprises quenching and tempering structures. 
     
     
         5 . The surface modified steel member of  claim 4 , wherein the quenching and tempering structures comprise tempered sorbate. 
     
     
         6 . The surface modified steel member of  claim 1 , wherein a thickness of the metallic diffusion layer is in a range from 30 microns to 120 microns, and a thickness of the alloy deposition layer is in a range from 60 microns to 110 microns. 
     
     
         7 . The surface modified steel member of  claim 1 , wherein a concentration of the pearlite crystals in the metallic diffusion layer decreases along a direction from the alloy deposition layer to the steel substrate, and a concentration of the ferrite crystals in the metallic diffusion layer increases along the direction from the alloy deposition layer to the steel substrate. 
     
     
         8 . The surface modified steel member of  claim 7 , wherein the concentration of the pearlite crystals in a region of the metallic diffusion layer facing the alloy deposition layer is in a range from 65% to 85%, and a concentration of the ferrite crystals in the region is in a range from 15% to 35%. 
     
     
         9 . A method for modifying surface of steel material, comprising:
 providing a steel substrate which is made of low-carbon steel or low-carbon alloy steel;   subjecting the steel substrate to pretreatment to clean surface of the steel substrate;   providing a penetrating agent, the penetrating agent comprising Zn powder in a range from 15% to 20% by weight, Ni powder in a range from 3% to 4% by weight, Al powder in a range from 2% to 2.5% by weight, rare earth metallic powder in a range from 2% to 3% by weight, ammonia chloride in a range from 1% to 4% by weight, and Al 2 O 3  powder in a remaining range by weight;   loading the steel substrate after the pretreatment and the penetrating agent into an enclosed steel container, heating the steel container to a temperature in a range from 370 degrees Celsius to 450 degrees Celsius, and rotating the steel container at a speed in a range from 5 RPM to 10 RPM during the heating, thereby causing the penetrating agent to penetrate into the steel substrate to modify the surface of the steel substrate;   washing the steel substrate after surface modification, thereby obtaining the surface modified steel member.   
     
     
         10 . The method of  claim 9 , wherein the pretreatment comprises cleaning of oil and grease adhering to the surface with alkaline solution, cleaning by ultrasonic waves, or by heating, and the pretreatment further comprises cleaning of rust on the surface by grit blasting. 
     
     
         11 . The method of  claim 9 , wherein the steel substrate is preheated before loading into the enclosed steel container, the preheated steel substrate and the penetrating agent are mixed followed by being loaded into the steel container. 
     
     
         12 . The method of  claim 9 , wherein the steel substrate and the penetrating agent are both at a room temperature when loaded into the steel substrate. 
     
     
         13 . The method of  claim 9 , wherein the steel substrate is quenched and tempered to form quenching and tempering structures on the steel substrate before the pretreatment. 
     
     
         14 . The method of  claim 9 , wherein a time period for heating the steel container is in a range from 1 hour to 10 hours. 
     
     
         15 . The method of  claim 9 , wherein the steel substrate after surface modification is naturally cooled before washing.