Standard martensitic stainless steel：403、410、414、416、416(Se)、420、431、440A、440B和440C type,the corrosion resistance of these steels comes from chromium，its range is from 11.5-18%，the higher chromium content of the steel need more carbon to ensure the formation of martensite during heat treatment，the above 440 three types stainless steel are rarely considered as the need for welding applications，and the 440 component of the molten metal is not easy to achieve.Standard martensitic steel modified, containing the class such as nickel,molybdenum,vanadium and other elements of the added , which is mainly used for the standard steel limited allowable operating temperature increased to higher than 1100K.When adding these elements ,carbon content was also increased, with the increase of carbon content in welding the heat affected zone sclerosis avoid cracking problems become more serious. Martensitic stainless steel can be annealed,hardened and tempered, no matter how the steel original state, martensitic zone will produce a hardening in the vicinity of the weld bead, the hardness of the heat affected zone is mainly determined by the carbon content of the base metal，toughness decreases when the hardness increases，and this area is relatively easy to crack，preheat and interpass temperature control, the most effective way to avoid cracking，in order to get the best properties,heat treatment is necessary. Martensitic stainless steel is a kind of stainless steel which can be adjusted by heat treatment (quenching and tempering)，in layman's terms ,is a kind of stainless steel can be hardened.This characteristic determines that this kind of steel must have two basic conditions：one is that there must exist the austenite phase in the equilibium phase diagram，long time heating is carried out in the temperature range of the region，after the carbide is dissolved in the steel,the martensite is formed after quenching，the chemical composition must be controlled in the gamma or alpha phase region，the other is to make the alloy corrosion resistance and oxidation of the passivation film，chrome content must be above 10.5% , according to the difference of the alloying elements ,it can be divided into martensite chromium stainless steel and martensite chromium nickel stainless steel.  The main alloying elements of martensitic chromium stainless are iron , chromium and carbon.  Fe-Cr system phase diagram of iron rich part，if Cr is more than 13%,  there is no gamma phase ，this kind of alloy is a single phase ferrite alloy，and can not produce marteniste in any heat treatment system. This must be included in the Fe-Cr two element alloy to join the austenite forming element ,in order to expand the gamma phase region.N 、C is an effective element for Martensitic chromium stainless steel.C、N element additions make the alloy allow for higher chromiun content. In

the martensitic chromium stainless steel, in addition to chromium, C is another most important essential element，in fact ,martensitic chromium stainless steel is a kind of heat resistant steel, chromium, carbon, three element alloy. Of course ,there are other elements. With the use  of  these elements,the general organization is determined by the Schaeffler chart. Martensitic stainless steel is mainly low carbon or high carbon steel with chrome content in the range of 12%-18%.Widely used martensitic steel has the following 3 categories：

1. Low carbon and medium carbon 13% Cr steel

2. High carbon 18% Cr steel

3.Low carbon nickel containing (about 2%) 17% Cr steel

Martensitic stainless steel with high strength and corrosion resistance ，which can be used to manufacture parts such as turbine blades (1Cr13),steam equipment shaft hinge and the pull rod (2Cr13), and working in corrosive medium parts such as valve,bolts(4Cr13),etc. High carbon steel(4Cr13,9Cr18)is suitable for the manufacture of medical devices, knives,measuring appliance,spring etc. Similar to ferritic stainless steel,other alloy elements can also be added to the martensitic stainless steel to improve other properties:

1.To add 0.07% S or Se to improve the machining performance ,such as 1Cr13S or 4Cr13Se；

2. Adding about 0.1% V and 1% Mo,the wear resisitance and corrosion resisitance of 9Cr18 steel can be increased；

3.By adding about 1 Mo-1W-0.2V, the thermal strength of 1Cr13 and 2Cr13 steel can be improved.

Martensitic stainless steel, as the same as the modulation of steel, can be used for quenching,tempering and annealing treatment. The mechanical

properties are similar to that of the modulated steel.,when the hardness is increased ,the tensile strength and yield strength are increased , while the

elongation,shrinkage and impact work are decreased. The corrosion resisitance  of martensitic stainless steel is mainly determined by the chromium content，the carbon in the steel and chromium carbide formed a stable chromium carbide, and indirectly affect the corrosion resistance of steel. In

13%Cr steel ,the lower the carbon content ,the higher the corrosion resisitance. In the 1Cr13,2Cr13,3Cr13 and 4Cr13 four kinds of steel, the

corrosion resistance and the strength of the order of the opposite. Smooth Technology Co.,Ltd will adopt international standards

SUM,SK7,SK5,MINIM,ZIN,SUS and other different materials for the design and production according to differrent functions,different structural requirement，to ensure that the structure of the shaft , functional , environmental protection ,low cost and mass production

feasibility.