Embrittlement steel

Holinski, R., Lubricant Diffusion Embrittles Steel Threads, Engineers Digest, p. 27, (March, 1983. ... 

Problem 4.10. Steel often contains trace amounts of Hj, which can lead to embrittlement. To avoid embrittlement, steel is often degassed prior to use in order to remove these trace H2 impurities. Degassing steel involves placing the steel in a vacuum, where the H2 concentration in the vacuum can be considered to be zero at all times. Degassing proceeds by three steps (1) solid-state diffusion of H2 from the steel bulk to the steel surface (2) desorption of H2 from the surface of the steel (3) gas-phase diffusion of the H2 away from the steel surface. 

Essentially, the two different methods by which hydrogen can embrittle steels... 

FIGURE 2 Typical differentiated Auger spectra taken from steels. The upper spectrum was from a nonembrittled (N.E.) steel, and the fracture surface that was analyzed was transgranular. The lower spectrum was from an embrittled steel, and the fracture surface that was analyzed was intergranular. [From Stein, D. F., Joshi, A., and LaForce, R. R (1969). ASM Trans. Q. 62, 776.]... 

Carbon content is usually about 0.15% but may be higher in bolting steels and hot-work die steels. Molybdenum content is usually between 0.5 and 1.5% it increases creep—mpture strength and prevents temper embrittlement at the higher chromium contents. In the modified steels, siUcon is added to improve oxidation resistance, titanium and vanadium to stabilize the carbides to higher temperatures, and nickel to reduce notch sensitivity. Most of the chromium—molybdenum steels are used in the aimealed or in the normalized and tempered condition some of the modified grades have better properties in the quench and tempered condition. 

Ferritic Stainless Steels. These steels are iron—chromium alloys not hardenable by heat treatment. In alloys having 17% chromium or more, an insidious embrittlement occurs in extended service around 475°C. This can be mitigated to some degree but not eliminated. They commonly include Types 405, 409, 430, 430F, and 446 (see Table 4) newer grades are 434, 436, 439, and 442. 

The low temperature impact strength of stmctural steels was found to be significantly improved with the additions of 0.022—0.008% Te. The low (—40° C) temperature impact strength of a steel annealed at blue brittie temperature of 350°C did not show any embrittlement effect with the addition of. 002% Te (76). 

The Tj-carbides are not specifically synthesized, but are of technical importance, occurring in alloy steels, stelUtes, or as embrittling phases in cemented carbides. Other complex carbides in the form of precipitates may form in multicomponent alloys or in high temperature reactor fuels by reaction between the fission products and the moderator graphite, ie, pyrographite-coated fuel kernels. 

Cathodic treatment of steel parts in acids could be expected to contribute significantly to hydrogen embrittlement of the part if the steel has been previously heat treated to over 40 HRC. Cold-worked steel is susceptible at a lower hardness. Some work shows more embrittlement from the plating bath than from preplate treatments (36). 

Analysis methods for hydrogen absorbed in the deposit have been described (65), and instmments are commercially available to detect hydrogen in metals. Several working tests have been devised that put plated specimens under strain and measure the time to failure. A method for cadmium-plated work has been described (66) as has a mechanical test method for evaluating treatments on AlSl 4340 Steel (67). Additional information on testing for hydrogen embrittlement is also available (68). 

Virtuallv evety alloy system has its specific environment conditions which will prodiice stress-corrosion cracking, and the time of exposure required to produce failure will vary from minutes to years. Typical examples include cracking of cold-formed brass in ammonia environments, cracking of austenitic stainless steels in the presence of chlorides, cracking of Monel in hydrofluosihcic acid, and caustic embrittlement cracking of steel in caustic solutions. 

In handhng caustic, as-welded steel can be used without developing caustic-embrittlement cracking if the temperature is below 50°C (I20°F). If the temperature is nigher and particularly if the concentration is above about 30 percent, cracking at and adjacent to non-stress-relieved welds frequently occurs. 

Figure 9.16 depicts the arrangement of connections in the extrusion barrel cooling jacket. Embrittlement and cracking of these stainless steel connections (Figs. 9.17 and 9.18) were occurring as frequently as every 4 to 6 weeks. 

Aikaiinity Bicarbonate (HCOs" ), carbonate (COs , and hydroxyl (OH ), expressed as CaCOs Foaming and carryover of solids with steam embrittlement of boiler steel bicarbonate and carbonate produce CO2 in steam, a source of corrosion Lime and lime-soda softening, acid treatment, hydrogen zeolite softening, demineralization, dealkalization by anion exchange, distillation, degasifying... 

With these definitions in mind, a systematic classification has been made. The various types of embrittlement found in refineries and petrochemical plant equipment, susceptible steels, basic causes, and common remedies are listed in the accompanying table. 

Fabrication and Erection. Embrittlement problems associated with forming, welding and heat treatment are included in this section, although in some instances the heat treatment is done by the steel manufacturer. 

By indirect embrittlement (reaction by-product, atomic hydrogen diffusing into the lattice of the steel)... 

---