ASTM A335 pipe - Pipe standard:P2 P5 P9 P11 P12 P22 P91 P92

With the continuous development of modern industry and science and technology, machinery manufacturing, the strength of the workpiece, the hardness, toughness, ductility, wear resistance, as well as a variety of other physical and chemical properties of the rising, carbon steel has not fully meet These requirements. Reasons:

(1) The       size is not too big of parts made from carbon steel. Otherwise, due to insufficient hardenability and can not meet the requirements of strength and ductility, toughness. Adding alloying elements to increase the hardenability. (2) made of carbon steel, the cutting tool can not meet the requirements of the cutting red rigid. Alloy tool steel, high-speed steel and carbide. (3) can not meet the requirements of the special properties of carbon steel, such as requiring heat resistance, low temperature resistance, corrosion resistance, strong magnetic or non-magnetic, special alloy steel can with these properties.
       
      

11.1        presence of alloying elements in the steel

11.1.1       alloying elements and the interaction of carbon steel, the formation of carbides present in the steel

Interaction of alloying elements in steel and carbon, they can be divided into two categories:

(1) does not carbide-forming elements (called non-carbide-forming elements), including nickel, silicon, aluminum, cobalt, copper, etc.. Since these elements and the binding force of the carbon is smaller than the iron, so in the steel, they can not and carbonized together, they are the carbides of the steel structure and no significant effect.

(2) carbide-forming elements (referred to as a carbide-forming element), based on the strength of their force to combine with carbon, the carbide-forming elements is divided into three categories.

1) weak carbide forming elements: manganese

    The manganese carbon binding force only slightly stronger than iron. Manganese added to the steel, and generally do not form special carbide (Structure and Fe3C different carbides called special carbide), but is dissolved in the cementite.

2) in the strong carbide forming elements; chromium, molybdenum, tungsten,

3) the strong carbide forming elements: vanadium, niobium, titanium

High stability, such as TiC l 000C quenching began to slow dissolution, these carbides have high hardness, for example, in the high-speed steel plus vanadium, forming the V4C make it higher abrasion resistance.

11.1.2       alloying elements dissolved in the ferritic or austenitic , in the form of a solid solution exists in the steel

11.1.3       alloying elements and the steel in the presence of nitrogen, oxygen, sulfur and other compounds, such as nitrides, oxides, sulfides and silicates in the form of nonmetallic inclusions in the steel

11.1.4       free state, that is not soluble iron, nor soluble compounds: lead, copper

11.2        alloy elements on the balance of steel organizations

Performance in changing the state diagram of the iron-carbon alloy

11.2.1 the       influence of the alloying elements on the critical temperature of the steel

Manganese, nickel, copper A3 line decreased, molybdenum, tungsten, silicon, vanadium A3 line increases. The same effect on A1 , a greater degree of influence,

11.2.2       alloying elements of the steel eutectoid point ( S point) position

Most alloy eutectoid point to the left, molybdenum and tungsten in the mass fraction of the eutectoid point shifted to the right.

11.2.3       of alloying elements on the size of the austenite phase region

11.2.3.1      expand γ District

Alloying elements and the γ -Fe α -Fe to form a solid solution, at room temperature for the austenitic microstructure. Ni, Mn

11.2.3.2      reduce γ District

Inhibition of F to A transition, Cr

11.3        of alloy elements on the influence of heat treatment

11.3.1       alloying elements austenitizing

Austenite grain in ferrite and carbide boundary nucleation and growth; remaining carbide dissolution; austenitic components

A uniform residence time at high temperature, austenite grains grow roughening process. Addition of alloying elements in steel after three processes have a greater impact.

(1)       containing a carbide-forming element of the alloy steel, carbide, their organization is more stable than cementite alloy cementite or special carbides, therefore, when the austenitization heating carbides less soluble i.e. require a higher temperature and longer time. Generally, alloying elements carbide forming tendency stronger and and its carbide is also more difficult to dissolve.

(2)       homogenization of the alloying elements in the austenite, and also requires a long time, because the diffusion rate of the alloying elements, which are much less than the diffusion rate of carbon.

(3)       certain alloying elements strongly hinder austenite grain coarsening process, which is mainly related to and alloy carbides difficult dissolved The undissolved carbides impede the austenite grain boundary migration, therefore, contain strong carbide forming elements (such as molybdenum, tungsten, vanadium, niobium, titanium, etc.), steel, austenitizing heating is easy to obtain the fine grain of the tissue.

Various alloying elements on the austenite grain coarsening process can generally be summarized as follows:

1) strong block the grain coarsening elements: titanium, niobium, vanadium, aluminum, etc., in which the strongest role of titanium.

2) the strong carbide forming elements tungsten, molybdenum, chromium, also significantly hinder austenite grain coarsening process.

3) is generally believed that the silicon and the nickel can also hinder the coarsening of austenite grains, but the effect is not obvious.

4) manganese and phosphorus in the austenite grain coarsening elements.

11.3.2       alloying elements on the austenite decomposition transformation

The majority of alloying elements austenite decomposition transformation slowed, C-curve to the right, is to improve the steel hardenability.

The influence of alloy elements on martensitic transformation

Increase the cooling time, to reduce the cooling rate.

In addition, the alloying elements on the martensitic transition temperature (Ms point ) also have a significant impact. Most of the alloy elements were the martensite transition temperature (Ms point ) lower, in which manganese, chromium, nickel role most strongly, only aluminum, cobalt is to raise the Ms point.